Geometry

An Open Cascade example file representing a generic F1-like open wheel race car was chosen as the basis for the geometry in this example simulation. Importing the race car into Caedium revealed a combination of faces and volumes.

Original Geometry

Using the various geometry creation and fixing tools in Caedium, the original geometry was modified in order to represent the volume of air surrounding the car. By assuming a symmetric car and flow field, only half of the flow volume is needed for the CFD simulation. Symmetry allows the simulation to run twice as quickly and only use half the memory that would otherwise be necessary.

The race car, its wheels, and the ground plane were specified as walls (impregnable by air). Additionally the wheels were assigned a rotational speed and the ground plane was configured with a linear speed matching the free-stream air speed. The sides and ceiling of the flow volume were specified as symmetry planes to simulate the other half of the flow volume and mimic free air. The upstream face was specified as an inlet and the downstream face was specified as an outlet.

Results

The mesh created in Caedium for this simulation contained 612,966 tetrahedral elements.

Surface Mesh

Lift and drag monitors were created to provide feedback as the simulation progressed and to determine whether the simulation was converged. These same monitors also reported the lift and drag values which are key factors in assessing the performance of a race car's aerodynamics.

Drag and Lift Monitors

Streamlines and contours were created to provide insights into the behavior of the airflow on the surface of the race car and in the wake behind it.

Velocity Magnitude Contours and Streamlines

Closeup of Wake Streamlines

Pressure Coefficient Contours

Conclusion

This example shows how Caedium can simulate the complex air flow around an open wheel race car with rotating wheels and moving ground. Note also that this type and size of simulation is well within the capabilities of Caedium running interactively on a regular desktop or laptop computer.

Comments

After performing some mesh refinement studies on rotating wheels it became evident that the mesh size around the wheels in the original simulation above was inadequate. Thus another simulation was run with the mesh refined in the rear-upper-quadrant on the wheels. Also continuous wall functions were used which are more tolerant of surface cell size variation than standard wall functions.

Results

The mesh created in Caedium for this simulation contained approximately 1.2 million tetrahedral elements.

Refined Surface Mesh

The streamlines around the wheels have a larger separation zone that extends towards the top of the wheel.

Refined Open Wheel Race Car Streamlines

The lift and drag forces remained unchanged from the original simulation.